Dendritic cells control the immune system from different vantage points. Dendritic cells control the responses of several types of lymphocytes; the transition between innate and adaptive immunity; the quality of the T cell response including Th1 polarization, memory, and even tolerance; and immunology in many clinical settings. This multidisciplinary meeting will develop the following areas: 1) vaccination and immune therapy, including the manipulation of dendritic cell function in vivo; 2) interactions of dendritic cells with microbial pathogens including the many innate functions of dendritic cells; 3) the early response of different types of lymphocytes to dendritic cells, and the organization of this response in vivo; 4) the role of dendritic cells in different forms of peripheral tolerance and the regulation of autoimmunity; 5) the specialized properties of dendritic cells in antigen handling, processing and presentation. As has been the case in prior Keystone Symposia on dendritic cells, there will be an equal number of presentations by invited speakers and speakers selected from the abstracts. The organizers have planned two coordinate meetings, the first entitled Dendritic Cells, Interfaces with Immunobiology & Medicine (March 5-10, 2003), and the second Cell Biology of the Immune Response (March 7-12, 2003). Each will be a four-day meeting, but will share joint sessions on the two overlapping days. This will provide an opportunity to bring together scientists interested in a valuable range of topics in immunology in general and dendritic cells in particular.